Investors punished global tech stocks on Monday after the emergence of a Chinese chatbot competitor to OpenAI's ChatGPT, DeepSeek, raised doubts about the sustainability of the US artificial intelligence boom. The tech-heavy Nasdaq index in New York opened lower after investors digested the implications of the latest AI model developed by the startup DeepSeek. Nvidia, the most valuable listed company in the US and a leading maker of the computer chips that power AI models, lost more than 400bn ( 321bn) in stock market value in early trading as its shares declined 13.6%, while Microsoft shed 130bn and Google's parent, Alphabet, declined by 80bn. Nvidia's fall – which wiped about 465bn off its value, was the biggest in US stock market history, according to Bloomberg. The DeepSeek AI assistant topped the Apple app store in the US and UK over the weekend, above OpenAI's ChatGPT.